异步序列组合子与背压控制

实现一套AsyncSequence组合子（merge、zip、buffer）并集成自定义背压策略防止数据堆积 · 难度：入门 · +10XP

异步序列组合子与背压控制

Swift的AsyncSequence提供了异步迭代能力，但缺少高级组合子。本教程构建AsyncMergeSequence、AsyncZipSequence与AsyncBufferedSequence，并引入基于令牌桶的背压控制，确保消费者与生产者速率匹配。

struct AsyncBufferedSequence<Base: AsyncSequence>: AsyncSequence {
    typealias Element = Base.Element
    let base: Base
    let maxBuffer: Int
    
    struct Iterator: AsyncIteratorProtocol {
        var buffer: [Element] = []
        var baseIterator: Base.AsyncIterator
        
        mutating func next() async throws -> Element? {
            while buffer.isEmpty, let new = try await baseIterator.next() {
                buffer.append(new)
                if buffer.count >= maxBuffer { break }
            }
            return buffer.isEmpty ? nil : buffer.removeFirst()
        }
    }
}